Preheat oven to 350 degrees. Grease a 13x9 pan and set aside.
Peel ripe bananas and place in a bowl. Use a fork or potato masher to mash until smooth.
Wet Ingredients: To the unsalted butter and sugar, add the eggs one at a time, mixing just until combined after each. Then add the sour cream, vanilla extract, and the mashed bananas.
Dry Ingredients: In a separate bowl, combine flour, a teaspoon of baking soda, brown sugar, and salt until combined.
Add this dry mixture to the wet in two additions. Use a gentle folding motion, scoop from the bottom of the bowl, and fold over.
Bake for 30-35 minutes, until the top is golden brown and a toothpick inserted in the center comes out clean. Cool completely.